Photothermic silver halide element containing an organic mercuric soap and a color forming coupler

ABSTRACT

LIGHT-SENSITIVE HEAT DEVELOPABLE SHEET MATERIALS CONTAINING ORGANIC SILVER SALT AND PHOTOSENSITIVE SILVER HALIDE AND CAPABLE ON EXPOSURE AND DEVELOPMENT OF FORMING CLEAR, BRIGHT AND INTENSE COLOR IMAGES CONTAIN BETWEEN .5 AND .9 EQUIVALENT OF MERCURY AND UP TO 11 MOLS OF COLOR COUPLER PER MOL OF SILVER AND ARE DEVELOPED BY HEATING IN PRESENCE OF A P-PHENYLENEDIAMINE REDUCING AGENT FOR SILVER ION.

United States Patent 3,764,328 PHOTOTI-IERMIC SILVER HALIDE ELEMENT CON- TAINING AN ORGANIC MERCURIC SOAP AND A COLOR-FORMING COUPLER Stephen P. Birkeland, White Bear Lake, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn. No Drawing. Filed Jan. 3, 1972, Ser. No. 215,084 Int. Cl. G03c 1/04, 1/52, 1/76 US. Cl. 96-67 11 Claims ABSTRACT OF THE DISCLOSURE Light-sensitive heat developable sheet materials containing organic silver salt and photosensitive silver halide and capable on exposure and development of forming clear, bright and intense color images contain between .5 and .9 equivalent of mercury and up to 11 mols of color coupler per mol of silver and are developed by heating in presence of a p-phenylenediamine reducing agent for silver ion.

This invention relates to the recording of light-images in color and to sheet materials useful therein. In one aspect the invention relates to sheet materials which, when merely exposed to a light-image and then uniformly briefly heated, display a corresponding visible image in color. In one particular aspect the invention relates to transparent sheet materials which may be thus exposed and heated to provide color projection transparencies.

Copy-sheets suitable for forming color images by dry photography have been described in US. Pat. No. 3,531,- 286. The light-sensitive color-forming coating contains a small amount of silver halide catalytically associated with a light-stable organic silver salt, a pphenylendiamine developer as a reducing agent for the silver salt, and a phenolic or active methylene color coupler component. Heating of the light-exposed sheet causes selective oxidation of the developer at light-struck areas and coupling of the resulting intermediate to form the color. At the same time, reduction of the silver salt results in the darkening of the image areas which therefore have a somewhat muddy appearance. As a result, such sheets do not provide clear color projection transparencies or bright color images without further treatment.

The addition of small amounts of mercuric compounds to copy-sheets useful in dry photography has been found, in US. Pat. No. 3,589,901, to make possible an image reversion such that darkening occurs primarily at unexposed rather than at light-exposed areas. The mercuric ion is conveniently added as mercuric halide which serves also as a source of halide ion for conversion of a small proportion of the silver salt to photosensitive silver halide. The bromide is preferred for general usage; the chloride is also effective, and mixtures of chloride or bromide with minor proportions of iodide are also useful for special purposes. Within certain limited proportions, the presence of the mercuric ion imparts a negative slope to the D log E curve and makes possible the desired image reversion. At both higher and lower proportions of mercuric ion the D log E curve has a positive slope and inversion of image does not occur.

Patented Oct. 9, 1973 The present invention likewise makes use of the principles of dry photography together with the use of a pphenylenediamine developer reducing agent and a color coupler, and of mercuric ion, to provide light-sensitive sheet materials with which either negative (inverted) or positive (reverted) images may be produced in clear bright color upon exposure to a light-image followed by heating. Surprisingly, the amount of mercuric ion required is found to be far in excess of that range shown by the prior art to provide a negative D log E slope. Furthermore, when the mercuric ion is added in the form of mercuric bromide or equivalent which then serves at the same time as the source of halide ions, the amount of halide ion thus introduced is far greater than required for optimum catalyst formation and in fact is within the approximate range of 50 to percent of that required for complete conversion of organic silver salt to silver halide. At least about ten percent of the total silver must be present in the form of the organic silver salt.

The photosensitive silver halide is normally prepared by mixing together one equivalent of an organic silver soap with a lesser amount, i.e. between about 0.5 and 0.9 equivalent, of halide ion. Where larger amounts of halide ion are employed, e.g. up to or percent of the organic soap, no useful images are formed; but such compositions and coatings may be again made capable of image formation by subsequent addition of free organic silver soap in amounts providing at least a ten percent excess over the total halide. However the procedure produces less dense images and slightly higher background for a given excess of organic silver soap than are provided by the previously described and presently preferred procedures.

The mercuric ion and halide ion need not be introduced in the form of mercuric halide but may instead be added separately, for example as mercuric acetate and as hydrogen bromide. In such case the amount of halide ion and of mercury ion will each still be equivalent to about 50 to 90 percent of the amount of silver ion although they will not necessarily be precisely equivalent to each other.

With compositions prepared, as above indicated, from an organic silver salt, a source of halide ion, a source of mercuric ion, a p-phenylendiamine developer, and a color coupler component, it has unexpectedly been found possible effectively to increase the ratio of color coupler to silver salt far beyond that found useful in US. Pat. No. 3,531,286, and to obtain clear, bright color images of greatly increased color intensity by simple dry photography techniques.

Quantities of color coupler amounting to about one mole per equivalent of total silver produce images useful for some purposes but of relatively low density. A preferred range is from about two to about four moles of color coupler per equivalent of silver; and much larger amounts, up to at least about ten or eleven moles per equivalent, have also been used.

Silver salts, developers, couplers, and binders as described in said Pat. No. 3,531,286 are useful in the practice of the invention. Silver behenate, i.e. the silver salt of commercial behenic acid, is a preferred light-stable organic silver salt; silver stearate is also useful. N,N-diethyl-p-phenylenediamine hydrochloride, N,N-diethyl-3- methyl-p-phenylenediamine hydrobromide, and N,N-diethyl-p-phenylenediamine trifluoroacetate are exemplary of the p-phenylenediamine developers, the trifluoroacetate salts providing-prints which are particularly free of backgrounding, Couplers or color formers which form colors with the intermediates formed by oxidation of such developers include l-phenyl-3-methyl-2-pyrazolin-5-one, 2- chloro-l-naphthol, l-hydroxy-Z-naphthoic acid butylamide, l-phenyl-3-amino-pyrazolin-5-one, Z-naphthoyl acetonitrile, and l-naphthoyl-acetonitrile. Vinyl resins, butadienestyrene resins, and cellulose derivatives have each served as inert binders, polyvinyl butyral being preferred. Spectral sensitization of the photosensitive coating may be achieved Where desired by incorporation of appropriate sensitizing dyes; examples are 3-allyl-5 [3-ethyl-(2-naphthoxazoylidene)-ethylidene] 1 phenyl 2 thiohydantoin, 3 ethyl S (1-methyl-2(lH)-pyridylidene) rhodanine, 2-p-dimethylaminostyryl 1 ethylpyridinium iodide, and dicyanine. Other materials may be added for special purposes as desired.

The following specific examples will serve further to illustrate the practice of the invention.

EXAMPLE 1 First coating:

Ethyl acetate, ml. 25 Silver behenate, gm. 0.5 Mercuric bromide, gm. 0.18 Color coupler, gm. 0.50 Sensitizer dye solution, ml. 1 Binder solution, gm.

The silver behenate is dispersed in the solvent. The remaining ingredients are added in the dark and the mixture is milled on a ball mill until smooth. It is then coated on 4 mil Mylar polyester film using a coating orifice of 3 mils, and permitted to dry, all under darkroom conditions. The sheet is clear and transparent, the sensitizer producing substantially no appearance of color.

The dye solution contains one-half part of merocyanine green sensitizer dye in 99.5 parts of chloroform. The binder solution contains parts of polyvinyl butyral resin in 85 parts of ethyl acetate. The color coupler is lphenyl-3-methyl-2pyrazolin-S-one. The sensitizer dye has the structural formula Second coating:

N,N diethyl-p-phenylenediamine hydrochloride,

gm. 2 Binder dispersion, ml. 25

The binder dispersion contains 15 parts of vinyl acetatevinyl pyrrolidone copolymer in 85 parts of water.

The mixture is applied over the first coat using an orifice of two mils and the coating is permitted to dry, again under darkroom conditions. The two layers bond together without mixing.

The completed product is exposed through a continuous tone step wedge to 10 meter-candle-second of light from an incandescent tungsten filament source. It is then heated at 75 C. for 10 seconds. A bright magenta image is obtained, with D 'of 0.9 and D of 0.18 determined'in conventional manner using green light. Unexposed areas are clear and substantially colorless.

"Sheets as thus prepared are found to give excellent color images when used shortly after manufacture but to have limited shelf life. Improved stability is obtained by isolating the reactants in separate sheets as in the following example.

EXAMPLE 2 i i i Light'sensitive sheet Com onent, arts y Weigl it p A B C D E F G Silver salt; .5 .5 .2 .3 .4 .3 .5 Mercun'c bromide 1 17 05 1 08 075 18 Binder 1. 5 3. 0 1. 5 1. 2 1. 5 1. 5 1. 5 Coupler .6 3.0 .3 .3 .4 .4 .5 Sensitizer 002 0005 001 001 0005 Image intensifie 3 025 Image color 0 C M M M M M Coupler/silver 3 3 5 2.25 2 3 2.5

In the above tabulation, silver behenate, is used in sheets A, B, E and G, silver stearate in the remainder. The binder is polyvinyl butyral in A, E, and G; butadienestyrene block copolymer in B and D; cellulose acetate butyrate in C; and polyvinyl pyrrolidone in F. Couplers are: A, 2 chloro-l-naphthol; B, l-hydroxy-Z-naphthoic acid butylamide; C, l-phenyl-3-methylpyrazolin-5-one; D, 1-phenyl-3-amino-pyrazolin-5-one; E, Z-naphthoyl acetonitrile; F, l phenyl-3-methyl-pyrazolin5-one; and G, 1- phenyl 3-methyl-2-pyrazolin-5-one. Phthalazinone serves as an image intensifier in sheets Band C. Solvents appropriate to the particular binder are used in mixing and coating the components; thus, ethyl acetate or a 3:2 mixture of toluene and ethanol may be used with polyvinyl butyral, toluene or tetrahydrofurane with butadiene-styrene, 1:1 acetone-methanol with cellulose acetate butyrate, and methanol with polyvinyl pyrrolidone.

As in Example 1, the remaining components are Well mixed with the silver salt slurry and the mixture is coated on a suitable backing, preferably a flexible film, and permitted to dry under dark conditions.

A color developer sheet is prepared from a mixture containing Silicone release agent (optional) (as required).

By coating on 3 mil Mylar polyester film at an orifice of 3 mils and drying the coated film. The light-sensitive sheets AG are each separately exposed to a light-image and then heated in face-to-face contact with a segment of the developer sheet. (The color developer sheet and light sensitive sheet may be held together in face-to-face contact as a unit.) Typically, heating for 10 seconds at about C. develops a brilliant color at the light-exposed areas, the remaining areas remaining substantially unchanged. For higher development temperatures, small amounts of silicone release agent in the color developer sheet coating are desirable to prevent picking or offsetting from the colored image areas. Sheets A and B give a cyan image, the others give a magenta image, as indicated in the table by letters C and M, under the conditions described. Images of other colors may be obtained by substitution of appropriate sensitizers and/or couplers; for example, a sheet similar to sheet G but containing a blue sensitizing 'dye and o-acetoacetanisidine coupler yields a brilliant yellow image, again with an unchanged background. Other compounds which result in yellow images include Z-benzoylacetanilide, oand p-bromo-acetoacetanilide, Z-methoxy- 4 methylacetoacetanilide. A suitable blue sensitizer is identified as having the structure In the foregoing examples the light-exposed areas of the sensitive sheet become colored during development, while the background remains unaffected, thus producing a negative image of the original. The opposite result may also be achieved, as will now be shown.

EXAMPLE 3 Light-sensitive sheet:

Ethyl acetate, ml 25-35 The components are mixed together and coated as described for the first coating in Example 1. The sheet is clear and transparent.

Developer sheet:

Methanol, ml. 40 Polyvinyl pyrrolidone, gm. 3 Catechol, gm. 2

The components are mixed by ball milling and coated on 3 mil Mylar polyester film at an orifice of 3 mils, followed by drying.

The light-sensitive sheet is given a 400 meter-candlesecond exposure through a transparency having an opaque image pattern. An open-mesh thin silk screen is placed over the exposed surface to serve as a porous separator web, followed by the developer sheet, and the composite is placed for seven seconds between metal platens heated to 125 C. A barely noticeable darkening occurs at the light-struck areas. The developer sheet and screen are removed and the sheet is flooded with light. It is then heated for seconds at 85 C. in face-to-face contact with a color developer sheet prepared as for Example 2. Areas of the sensitive sheet corresponding to the opaque image pattern of the original transparency are converted to a magenta color; the background areas remain substantially unchanged.

By adding a reducing agent for silver ion directly to the light-sensitive sheet coating, the need for a separate first developer sheet is obviated. As an example, the cantious addition of 0.6 gm. of hydroquinone to the coating composition immediately preceding the spreading and drying of the composition in making the light-sensitive sheet permits desensitization at light-struck areas of the sheet by simply heating the sheet after exposure.

In a further modification the coating composition for the light-sensitive sheet contains 0.2 gm. of tetrahydrophthalimide in place of phthalazinone and 1.0 gm. of 2-chloro-1-naphthol in place of the p-nitrophenylacetonitrile and hydroquinone, and is coated on a white opaque film of polyethylene terephthalate polyester pigmented with titanium dioxide. Exposure to a light-image followed by heat development yields a faint yellowish-brown discoloration at light-exposed areas, a portion of the chloronaphthol serving in this step as a developer. Flooding the surface with light, followed by heating against the color developer sheet of Example 2, produces an intense cyan color at the initially non-exposed areas which is particularly brilliant against the white backing.

The previous examples have resulted in monocolor prints. Multi-color prints are also possible as will now be illustrated.

EXAMPLE 4 Three mil transparent polyester film is coated over one surface with a light-sensitive composition similar to that of Example 3 but containing 0.25 rather than 0.2 gm. of phthalazinone and substituting 1-phenyl-3-methyl- 2-pyrazolin-5-one for the p-nitrophenylacetonitrile. The opposite surface is similarly coated but substituting N-phenyl-benzoylacetamide and in the amount of 0.6

gm. Additionally the first coating contains a green sensitizer dye and the second coating contains a blue sensitizer dye. The light-sensitive film thus produced is exposed through a tricolor negative transparency to metercandle-seconds of tungsten radiation and is heated between two sheets of color developer film as described under Example 2 to develop the color images. A magenta image is developed in the first coating and a yellow image in the second.

Other color combinations are available. As an example, l-cyanoacetyl naphthalene with the blue sensitizer of the above second coating yields as orange color, and l-hydroxy-Z-(N-butyl)naphthamide with a red sensitizer yields a blue-green color. A useful red sensitizer has the structure Analogous results are obtainable using the image reversal process, coatings, and developer sheets of Example 3.

What is claimed is as follows:

1. Method of making a light-sensitive sheet material which is adapted to become colored when first exposed to light and then heated in the presence of a p-phenylenediamine developer, said method comprising blending together, in an inert volatile liquid vehicle containing a binder, components consisting essentially of normally light-stable organic silver salt, a source of mercuric ions and a source of halide ions, and a phenolic or activemethylene color-forming coupler, and forming from the resulting blend a thin uniform dried coating on a supporting sheet material, the molar ratios of said components being so selected as to provide, for each equivalent weight of said silver salt, from about .5 to about .9 equivalent weight of each of said mercuric ions and halide ions, and at least one molecular weight of said coupler.

2. Method of claim 1 wherein the coupler is present in an amount of from about two to about eleven moles per mole of silver salt.

3. Light-sensitive sheet material adapted to become colored when first exposed to light and then heated in the presence of a p-phenylenediamine developer and includ ing a light-sensitive layer containing about 0.5 to about 0.1 equivalent of organic silver soap, correspondingly about 0.5 to about 0.9 equivalent of photosensitive silver halide and about 0.5 to about 0.9 equivalent of organic mercuric soap, and at least about one mole of phenolic or active methylene color-forming coupler.

. 4. Light-sensitive sheet material of claim 3 including in a separate second layer a reducing agent for silver ion.

5. Light-sensitive sheet material of claim 3 wherein said reducing agent is a p-phenylenediamine developer.

6. A unit including a light-sensitive sheet material as defined in claim 3 in face-to-face contact with a developer sheet containing a p-phenylenediamine reducing agent for silver ion.

7. A unit including a light-sensitive sheet material as defined in claim 4 wherein said reducing agent is other than a p-phenylenediamine developer, in face to-face contact with a developer sheet containing a p-phenylene diamine reducing agent for silver ion.

8. Light-sensitive sheet material of claim 3 wherein is included a reducing agent for silver ion.

9. Light-sensitive sheet material of claim 8 wherein said coupler is a reducing agent for silver ion.

10. Light-sensitive sheet material of claim 5 wherein said developer is a trifluoroacetate salt.

11. Light-sensitive sheet material of claim 3 wherein said light-sensitive layer is supported on one surface of 7 8 a transparent carrier having on its opposite surface a 3,589,903 6/1971 Birkeland 96--67 similar light-sensitive layer containing a different color 3,692,526 9/ 1972 Ulbing 9'6--1'14.1 coupler.

R f e Ci d NORMAN G. TORCHIN, Primary Examiner UNITED STATES PATENTS 5 W. H. LOUIE, IR., Assistant Examiner 2,637,657 5/1953 Ozols 117--36.8 3,531,286 9/1970 Renfrew 96114.1 CL

3,589,901 6/1971 Lyons 96-64 9675, 114.1; 117-368, 36.9 

